[thirdparty/gcc.git] / libstdc++-v3 / docs / html / configopts.html

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   <meta name="AUTHOR" content="pme@gcc.gnu.org (Phil Edwards)" />
   <meta name="KEYWORDS" content="libstdc++, libstdc++-v3, GCC, g++" />
   <meta name="DESCRIPTION" content="Configuration options for libstdc++-v3." />
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   <title>libstdc++-v3 configure options</title>
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<h1 class="centered"><a name="top">Interesting <code>configure</code>
options</a></h1>

<p class="fineprint"><em>
   The latest version of this document is always available at
   <a href="http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html">
   http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html</a>.
</em></p>

<p><em>
   To the <a href="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</a>.
</em></p>

<!-- ####################################################### -->
<hr />
<p>Here are some of the non-obvious options to libstdc++'s configure.
   Keep in mind that
   <!-- This SECnn should be the "Choosing Package Options" section. -->
   <a href="http://www.gnu.org/software/autoconf/manual/autoconf-2.57/html_node/autoconf_131.html#SEC131">they
   all have opposite forms as well</a>
   (enable/disable and with/without).  The defaults are for <strong>current
   development sources</strong>, which may be different than those for
   released versions.
</p>
<p>The canonical way to find out the configure options that are
   available for a given set of libstdc++ sources is to go to the
   source directory and then type:<code>  ./configure --help</code>
</p>

<dl>
 <dt><code>--enable-multilib  </code>[default]</dt>
 <dd><p>This is part of the generic multilib support for building cross
        compilers.  As such, targets like &quot;powerpc-elf&quot; will have
        libstdc++ built many different ways:  &quot;-msoft-float&quot;
        and not, etc.  A different libstdc++ will be built for each of
        the different multilib versions.  This option is on by default.
     </p>
 </dd>

 <dt><code>--enable-sjlj-exceptions  </code></dt>
 <dd><p>Forces old, set-jump/long-jump exception handling model.  If
        at all possible, the new, frame unwinding exception handling routines
        should be used instead, as they significantly reduce both
        runtime memory usage and executable size. This option can
        change the library ABI.
     </p>
 </dd>

 <dt><code>--enable-version-specific-runtime-libs  </code></dt>
 <dd><p>Specify that run-time libraries should be installed in the
        compiler-specific subdirectory (i.e.,
        <code>${libdir}/gcc-lib/${target_alias}/${gcc_version}</code>)
        instead of <code>${libdir}</code>.  This option is useful if you
        intend to use several versions of gcc in parallel.  In addition,
        libstdc++'s include files will be installed in
        <code>${libdir}/gcc-lib/${target_alias}/${gcc_version}/include/g++</code>,
        unless you also specify
       <code>--with-gxx-include-dir=<em>dirname</em></code> during configuration.
     </p>
 </dd>

 <dt><code>--with-gxx-include-dir=&lt;include-files dir&gt;</code></dt>
 <dd><p>Adds support for named libstdc++ include directory.  For instance,
        the following puts all the libstdc++ headers into a directory
        called &quot;2.97-20001008&quot; instead of the usual
        &quot;c++/(version)&quot;.
     </p>
        <pre>
   --with-gxx-include-dir=/foo/H-x86-gcc-3-c-gxx-inc/include/2.97-20001008</pre> </dd>

 <dt><code>--enable-cstdio  </code></dt>
 <dd><p>This is an abbreviated form of <code>'--enable-cstdio=stdio'</code>
        (described next). This option can change the library ABI.
     </p>
 </dd>

 <dt><code>--enable-cstdio=OPTION  </code></dt>
 <dd><p>Select a target-specific I/O package. At the moment, the only
        choice is to use 'stdio', a generic &quot;C&quot; abstraction.
        The default is 'stdio'.  A longer explanation is <a
        href="explanations.html#cstdio">here</a>.
     </p>
 </dd>

 <dt><code>--enable-clocale  </code></dt>
 <dd><p>This is an abbreviated form of <code>'--enable-clocale=generic'</code>
        (described next). This option can change the library ABI.
     </p>
 </dd>

 <dt><code>--enable-clocale=OPTION  </code></dt>
 <dd><p>Select a target-specific underlying locale package.  The
        choices are 'ieee_1003.1-2001' to specify an X/Open, Standard Unix
        (IEEE Std. 1003.1-2001) model based on langinfo/iconv/catgets,
        'gnu' to specify a model based on functionality from the GNU C
        library (langinfo/iconv/gettext) (from <a
        href="http://sources.redhat.com/glibc/">glibc</a>, the GNU C
        library), or 'generic' to use a generic &quot;C&quot;
        abstraction which consists of &quot;C&quot; locale info.
     </p>

     <p>As part of the configuration process, the "C" library is
      probed both for sufficient vintage, and installed locale
      data. If either of these elements are not present, the C++
      locale model default to 'generic.' On glibc-based systems of
      version 2.2.5 and above with installed locale files, 'gnu' is
      automatically selected.
     </p>
 </dd>

 <dt><code>--enable-libstdcxx-allocator  </code></dt>
 <dd><p>This is an abbreviated form of
        <code>'--enable-libstdcxx-allocator=auto'</code> (described
        next). This option can change the library ABI.
     </p>
 </dd>

 <dt><code>--enable-libstdcxx-allocator=OPTION  </code></dt>
 <dd><p>Select a target-specific underlying std::allocator.  The
        choices are 'new' to specify a wrapper for new, 'malloc' to
        specify a wrapper for malloc, 'mt' for a fixed power of two allocator
        (<a href="ext/mt_allocator.html">documented</a> under extensions),
	'pool' for the SGI pooled allocator or 'bitmap' for a bitmap allocator.
	This option can change the library ABI.
     </p>
 </dd>

 <dt><code>--enable-cheaders=OPTION  </code></dt>
 <dd><p>This allows the user to define what kind of C headers are
        used.  Options are c and c_std.  These correspond to the source
	directory's include/c and include/c_std.  The default is c_std.
     </p>
 </dd>

 <dt><code>--enable-threads  </code></dt>
 <dd><p>This is an abbreviated form of <code>'--enable-threads=yes'</code>
        (described next). This option can change the library ABI.
     </p>
 </dd>

 <dt><code>--enable-threads=OPTION  </code></dt>
 <dd><p>Select a threading library.  A full description is given in the
        general <a href="http://gcc.gnu.org/install/configure.html">compiler
        configuration instructions</a>.
     </p>
 </dd>

 <dt><code>--enable-libstdcxx-debug  </code></dt>
 <dd><p>Build separate debug libraries in addition to what is normally built.
        By default, the debug libraries are compiled with 
        <code> CXXFLAGS='-g3 -O0'</code>
        , are installed in <code>${libdir}/debug</code>, and have the
        same names and versioning information as the non-debug
        libraries. This option is off by default.
     </p>
     <p>Note this make command, executed in
        the build directory, will do much the same thing, without the
        configuration difference and without building everything twice: 
        <code>make CXXFLAGS='-g3 -O0' all</code>
     </p>
 </dd>

 <dt><code>--enable-libstdcxx-debug-flags=FLAGS</code></dt>

 <dd><p>This option is only valid when <code> --enable-debug </code>
        is also specified, and applies to the debug builds only. With
        this option, you can pass a specific string of flags to the
        compiler to use when building the debug versions of libstdc++.
        FLAGS is a quoted string of options, like
     </p>
        <pre>
  --enable-libstdcxx-debug-flags='-g3 -O1 -gdwarf-2'</pre>
 </dd>

 <dt><code>--enable-cxx-flags=FLAGS</code></dt>
 <dd><p>With this option, you can pass a string of -f (functionality)
        flags to the compiler to use when building libstdc++. This
        option can change the library ABI. FLAGS is a quoted string of
        options, like
     </p>
        <pre>
  --enable-cxx-flags='-fvtable-gc -fomit-frame-pointer -ansi'</pre>
     <p>
        Note that the flags don't necessarily have to all be -f flags,
        as shown, but usually those are the ones that will make sense
        for experimentation and configure-time overriding.
     </p>
     <p>The advantage of --enable-cxx-flags over setting CXXFLAGS in
        the 'make' environment is that, if files are automatically
        rebuilt, the same flags will be used when compiling those files
        as well, so that everything matches.
     </p>
     <p>Fun flags to try might include combinations of
     </p>
        <pre>
  -fstrict-aliasing
  -fno-exceptions
  -ffunction-sections
  -fvtable-gc</pre>
     <p>and opposite forms (-fno-) of the same.  Tell us (the libstdc++
        mailing list) if you discover more!
     </p>
 </dd>

 <dt><code>--enable-c99  </code></dt>
 <dd><p>The &quot;long long&quot; type was introduced in C99, along
        with many other functions for wide characters, and math
        classification macros, etc.  If enabled, all C99 functions not
        specified by the C++ standard will be put into <code>namespace
        __gnu_cxx</code>, and then all these names will
        be injected into namespace std, so that C99 functions can be
        used &quot;as if&quot; they were in the C++ standard (as they
        will eventually be in some future revision of the standard,
        without a doubt).  By default, C99 support is on, assuming the
        configure probes find all the necessary functions and bits
        necessary. This option can change the library ABI.
    </p>
 </dd>

 <dt><code>--enable-wchar_t  </code>[default]</dt>
 <dd><p>Template specializations for the &quot;wchar_t&quot; type are
        required for wide character conversion support.  Disabling
        wide character specializations may be expedient for initial
        porting efforts, but builds only a subset of what is required by
        ISO, and is not recommended.  By default, this option is on.
        This option can change the library ABI.
     </p>
 </dd>

 <dt><code>--enable-long-long  </code></dt>
 <dd><p>The &quot;long long&quot; type was introduced in C99.  It is
        provided as a GNU extension to C++98 in g++.  This flag builds
        support for &quot;long long&quot; into the library (specialized
        templates and the like for iostreams).  This option is on by default:
        if enabled, users will have to either use the new-style &quot;C&quot;
        headers by default (i.e., &lt;cmath&gt; not &lt;math.h&gt;)
        or add appropriate compile-time flags to all compile lines to
        allow &quot;C&quot; visibility of this feature (on GNU/Linux,
        the flag is -D_ISOC99_SOURCE, which is added automatically via
        CPLUSPLUS_CPP_SPEC's addition of _GNU_SOURCE).
        This option can change the library ABI. 
     </p>
 </dd>

 <dt><code>--enable-fully-dynamic-string  </code></dt>
 <dd><p>This option enables a special version of basic_string avoiding
        the optimization that allocates empty objects in static memory.
	Mostly useful together with shared memory allocators, see PR
	libstdc++/16612 for details.
     </p>
 </dd>

 <dt><code>--enable-concept-checks  </code></dt>
 <dd><p>This turns on additional compile-time checks for instantiated
        library templates, in the form of specialized templates,
        <a href="19_diagnostics/howto.html#3">described here</a>.  They
        can help users discover when they break the rules of the STL, before
        their programs run.
     </p>
 </dd>

 <dt><code>--enable-symvers[=style]  </code></dt>

 <dd><p>In 3.1 and later, tries to turn on symbol versioning in the
        shared library (if a shared library has been
        requested). Values for 'style' that are currently supported
        are 'gnu', 'gnu-versioned-namespace', 'darwin', and
        'darwin-export'. Both gnu- options require that a recent
        version of the GNU linker be in use. Both darwin options are
        equivalent. With no style given, the configure script will try
        to guess if the 'gnu' style can be used, and if so, will turn
        it on.
     </p>

 </dd>

 <dt><code>--enable-libstdcxx-pch  </code></dt>
 <dd><p>In 3.4 and later, tries to turn on the generation of
        stdc++.h.gch, a pre-compiled file including all the standard
        C++ includes. If enabled (as by default), and the compiler
        seems capable of passing the simple sanity checks thrown at
        it, try to build stdc++.h.gch as part of the make process. 
        In addition, this generated file is used later on (by appending <code>
        --include bits/stdc++.h </code> to CXXFLAGS) when running the
        testsuite.
     </p>
 </dd>

 <dt><code>--disable-hosted-libstdcxx  </code></dt>
 <dd><p>By default, a complete <em>hosted</em> C++ library is built.  The
        C++ Standard also describes a <em>freestanding</em> environment,
        in which only a minimal set of headers are provided.  This option
        builds such an environment.
     </p>
 </dd>
</dl>
<p>Return <a href="#top">to the top of the page</a> or
   <a href="http://gcc.gnu.org/libstdc++/">to the libstdc++ homepage</a>.
</p>


<!-- ####################################################### -->

<hr />
<p class="fineprint"><em>
See <a href="17_intro/license.html">license.html</a> for copying conditions.
Comments and suggestions are welcome, and may be sent to
<a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>.
</em></p>


</body>
</html>
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ba43f4eb JW	1	<?xml version="1.0" encoding="ISO-8859-1"?>
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	6	<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
5d5e5e4e	7	<head>
64a6f971 JW	8	<meta name="AUTHOR" content="pme@gcc.gnu.org (Phil Edwards)" />
	9	<meta name="KEYWORDS" content="libstdc++, libstdc++-v3, GCC, g++" />
	10	<meta name="DESCRIPTION" content="Configuration options for libstdc++-v3." />
	11	<meta name="GENERATOR" content="vi and eight fingers" />
5d5e5e4e	12	<title>libstdc++-v3 configure options</title>
bc225f98 JW	13	<link rel="StyleSheet" href="lib3styles.css" type="text/css" />
bc225f98 JW	14	<link rel="Copyright" href="17_intro/license.html" type="text/html" />
5d5e5e4e PE	15	</head>
5d5e5e4e PE	16	<body>
b2dad0e3	17
0435269a	18	<h1 class="centered"><a name="top">Interesting <code>configure</code>
5d5e5e4e	19	options</a></h1>
b2dad0e3	20
21c93c39 JW	21	<p class="fineprint"><em>
21c93c39 JW	22	The latest version of this document is always available at
5d5e5e4e PE	23	<a href="http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html">
5d5e5e4e PE	24	http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html</a>.
21c93c39	25	</em></p>
b2dad0e3	26
21c93c39 JW	27	<p><em>
	28	To the <a href="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</a>.
	29	</em></p>
b2dad0e3 BK	30
b2dad0e3 BK	31	<!-- ####################################################### -->
64a6f971	32	<hr />
5d5e5e4e	33	<p>Here are some of the non-obvious options to libstdc++'s configure.
b2dad0e3	34	Keep in mind that
dcfa0bc8	35	<!-- This SECnn should be the "Choosing Package Options" section. -->
b80ec515	36	<a href="http://www.gnu.org/software/autoconf/manual/autoconf-2.57/html_node/autoconf_131.html#SEC131">they
5d5e5e4e	37	all have opposite forms as well</a>
20c176ab PE	38	(enable/disable and with/without). The defaults are for <strong>current
	39	development sources</strong>, which may be different than those for
	40	released versions.
5d5e5e4e PE	41	</p>
5d5e5e4e PE	42	<p>The canonical way to find out the configure options that are
8901ac21	43	available for a given set of libstdc++ sources is to go to the
5d5e5e4e	44	source directory and then type:<code> ./configure --help</code>
1860e6ab	45	</p>
8901ac21	46
5d5e5e4e	47	<dl>
64a6f971	48	<dt><code>--enable-multilib </code>[default]</dt>
5d5e5e4e	49	<dd><p>This is part of the generic multilib support for building cross
60ade935 PE	50	compilers. As such, targets like "powerpc-elf" will have
	51	libstdc++ built many different ways: "-msoft-float"
	52	and not, etc. A different libstdc++ will be built for each of
	53	the different multilib versions. This option is on by default.
5d5e5e4e	54	</p>
64a6f971	55	</dd>
b2dad0e3	56
f7be2549 BK	57	<dt><code>--enable-sjlj-exceptions </code></dt>
	58	<dd><p>Forces old, set-jump/long-jump exception handling model. If
	59	at all possible, the new, frame unwinding exception handling routines
	60	should be used instead, as they significantly reduce both
	61	runtime memory usage and executable size. This option can
	62	change the library ABI.
	63	</p>
	64	</dd>
	65
	66	<dt><code>--enable-version-specific-runtime-libs </code></dt>
	67	<dd><p>Specify that run-time libraries should be installed in the
	68	compiler-specific subdirectory (i.e.,
	69	<code>${libdir}/gcc-lib/${target_alias}/${gcc_version}</code>)
	70	instead of <code>${libdir}</code>. This option is useful if you
	71	intend to use several versions of gcc in parallel. In addition,
	72	libstdc++'s include files will be installed in
	73	<code>${libdir}/gcc-lib/${target_alias}/${gcc_version}/include/g++</code>,
	74	unless you also specify
	75	<code>--with-gxx-include-dir=<em>dirname</em></code> during configuration.
	76	</p>
	77	</dd>
	78
	79	<dt><code>--with-gxx-include-dir=<include-files dir></code></dt>
	80	<dd><p>Adds support for named libstdc++ include directory. For instance,
	81	the following puts all the libstdc++ headers into a directory
	82	called "2.97-20001008" instead of the usual
6aa43d99	83	"c++/(version)".
f7be2549 BK	84	</p>
	85	<pre>
	86	--with-gxx-include-dir=/foo/H-x86-gcc-3-c-gxx-inc/include/2.97-20001008</pre> </dd>
	87
64a6f971	88	<dt><code>--enable-cstdio </code></dt>
5d5e5e4e	89	<dd><p>This is an abbreviated form of <code>'--enable-cstdio=stdio'</code>
f7be2549	90	(described next). This option can change the library ABI.
5d5e5e4e	91	</p>
64a6f971	92	</dd>
b2dad0e3	93
f7be2549	94	<dt><code>--enable-cstdio=OPTION </code></dt>
58ac1d7f BK	95	<dd><p>Select a target-specific I/O package. At the moment, the only
	96	choice is to use 'stdio', a generic "C" abstraction.
	97	The default is 'stdio'. A longer explanation is <a
	98	href="explanations.html#cstdio">here</a>.
5d5e5e4e	99	</p>
64a6f971	100	</dd>
b2dad0e3	101
64a6f971	102	<dt><code>--enable-clocale </code></dt>
5d5e5e4e	103	<dd><p>This is an abbreviated form of <code>'--enable-clocale=generic'</code>
f7be2549	104	(described next). This option can change the library ABI.
5d5e5e4e	105	</p>
64a6f971	106	</dd>
8d66b99a	107
f7be2549	108	<dt><code>--enable-clocale=OPTION </code></dt>
5d5e5e4e	109	<dd><p>Select a target-specific underlying locale package. The
1fa4bed7 BK	110	choices are 'ieee_1003.1-2001' to specify an X/Open, Standard Unix
1fa4bed7 BK	111	(IEEE Std. 1003.1-2001) model based on langinfo/iconv/catgets,
33590f13	112	'gnu' to specify a model based on functionality from the GNU C
64a6f971	113	library (langinfo/iconv/gettext) (from <a
0435269a	114	href="http://sources.redhat.com/glibc/">glibc</a>, the GNU C
33590f13	115	library), or 'generic' to use a generic "C"
f7be2549	116	abstraction which consists of "C" locale info.
5d5e5e4e	117	</p>
0214010c	118
f7be2549 BK	119	<p>As part of the configuration process, the "C" library is
	120	probed both for sufficient vintage, and installed locale
	121	data. If either of these elements are not present, the C++
	122	locale model default to 'generic.' On glibc-based systems of
	123	version 2.2.5 and above with installed locale files, 'gnu' is
	124	automatically selected.
5d5e5e4e	125	</p>
64a6f971	126	</dd>
b2dad0e3	127
8b0d6051 BK	128	<dt><code>--enable-libstdcxx-allocator </code></dt>
	129	<dd><p>This is an abbreviated form of
	130	<code>'--enable-libstdcxx-allocator=auto'</code> (described
	131	next). This option can change the library ABI.
	132	</p>
	133	</dd>
	134
	135	<dt><code>--enable-libstdcxx-allocator=OPTION </code></dt>
	136	<dd><p>Select a target-specific underlying std::allocator. The
	137	choices are 'new' to specify a wrapper for new, 'malloc' to
	138	specify a wrapper for malloc, 'mt' for a fixed power of two allocator
638004cc PC	139	(<a href="ext/mt_allocator.html">documented</a> under extensions),
	140	'pool' for the SGI pooled allocator or 'bitmap' for a bitmap allocator.
	141	This option can change the library ABI.
8b0d6051 BK	142	</p>
	143	</dd>
	144
64a6f971	145	<dt><code>--enable-cheaders=OPTION </code></dt>
5d5e5e4e	146	<dd><p>This allows the user to define what kind of C headers are
1165dc50 PC	147	used. Options are c and c_std. These correspond to the source
1165dc50 PC	148	directory's include/c and include/c_std. The default is c_std.
5d5e5e4e	149	</p>
64a6f971	150	</dd>
99246c90	151
64a6f971	152	<dt><code>--enable-threads </code></dt>
5d5e5e4e	153	<dd><p>This is an abbreviated form of <code>'--enable-threads=yes'</code>
f7be2549	154	(described next). This option can change the library ABI.
5d5e5e4e	155	</p>
64a6f971	156	</dd>
b2dad0e3	157
f7be2549	158	<dt><code>--enable-threads=OPTION </code></dt>
572cd73a PE	159	<dd><p>Select a threading library. A full description is given in the
	160	general <a href="http://gcc.gnu.org/install/configure.html">compiler
	161	configuration instructions</a>.
5d5e5e4e	162	</p>
64a6f971	163	</dd>
b2dad0e3	164
d8d81f62	165	<dt><code>--enable-libstdcxx-debug </code></dt>
6aa43d99	166	<dd><p>Build separate debug libraries in addition to what is normally built.
3660e02f	167	By default, the debug libraries are compiled with
6aa43d99 BK	168	<code> CXXFLAGS='-g3 -O0'</code>
	169	, are installed in <code>${libdir}/debug</code>, and have the
	170	same names and versioning information as the non-debug
	171	libraries. This option is off by default.
21c93c39 JW	172	</p>
21c93c39 JW	173	<p>Note this make command, executed in
6aa43d99 BK	174	the build directory, will do much the same thing, without the
	175	configuration difference and without building everything twice:
	176	<code>make CXXFLAGS='-g3 -O0' all</code>
6aa43d99 BK	177	</p>
	178	</dd>
	179
d8d81f62	180	<dt><code>--enable-libstdcxx-debug-flags=FLAGS</code></dt>
6aa43d99 BK	181
	182	<dd><p>This option is only valid when <code> --enable-debug </code>
	183	is also specified, and applies to the debug builds only. With
	184	this option, you can pass a specific string of flags to the
	185	compiler to use when building the debug versions of libstdc++.
	186	FLAGS is a quoted string of options, like
	187	</p>
	188	<pre>
d8d81f62	189	--enable-libstdcxx-debug-flags='-g3 -O1 -gdwarf-2'</pre>
6aa43d99 BK	190	</dd>
6aa43d99 BK	191
64a6f971	192	<dt><code>--enable-cxx-flags=FLAGS</code></dt>
5d5e5e4e	193	<dd><p>With this option, you can pass a string of -f (functionality)
f7be2549 BK	194	flags to the compiler to use when building libstdc++. This
	195	option can change the library ABI. FLAGS is a quoted string of
	196	options, like
1860e6ab	197	</p>
0435269a PE	198	<pre>
0435269a PE	199	--enable-cxx-flags='-fvtable-gc -fomit-frame-pointer -ansi'</pre>
1860e6ab	200	<p>
b2dad0e3 BK	201	Note that the flags don't necessarily have to all be -f flags,
	202	as shown, but usually those are the ones that will make sense
	203	for experimentation and configure-time overriding.
5d5e5e4e PE	204	</p>
5d5e5e4e PE	205	<p>The advantage of --enable-cxx-flags over setting CXXFLAGS in
777c9517	206	the 'make' environment is that, if files are automatically
b2dad0e3 BK	207	rebuilt, the same flags will be used when compiling those files
b2dad0e3 BK	208	as well, so that everything matches.
5d5e5e4e PE	209	</p>
5d5e5e4e PE	210	<p>Fun flags to try might include combinations of
1860e6ab	211	</p>
0435269a	212	<pre>
b2dad0e3	213	-fstrict-aliasing
777c9517	214	-fno-exceptions
b2dad0e3	215	-ffunction-sections
0435269a	216	-fvtable-gc</pre>
1860e6ab	217	<p>and opposite forms (-fno-) of the same. Tell us (the libstdc++
0435269a	218	mailing list) if you discover more!
5d5e5e4e	219	</p>
64a6f971	220	</dd>
58fdec72	221
f7be2549 BK	222	<dt><code>--enable-c99 </code></dt>
	223	<dd><p>The "long long" type was introduced in C99, along
	224	with many other functions for wide characters, and math
	225	classification macros, etc. If enabled, all C99 functions not
	226	specified by the C++ standard will be put into <code>namespace
	227	__gnu_cxx</code>, and then all these names will
	228	be injected into namespace std, so that C99 functions can be
	229	used "as if" they were in the C++ standard (as they
	230	will eventually be in some future revision of the standard,
	231	without a doubt). By default, C99 support is on, assuming the
	232	configure probes find all the necessary functions and bits
	233	necessary. This option can change the library ABI.
	234	</p>
	235	</dd>
	236
347669a0 BK	237	<dt><code>--enable-wchar_t </code>[default]</dt>
	238	<dd><p>Template specializations for the "wchar_t" type are
	239	required for wide character conversion support. Disabling
	240	wide character specializations may be expedient for initial
	241	porting efforts, but builds only a subset of what is required by
	242	ISO, and is not recommended. By default, this option is on.
	243	This option can change the library ABI.
f7be2549 BK	244	</p>
	245	</dd>
	246
	247	<dt><code>--enable-long-long </code></dt>
	248	<dd><p>The "long long" type was introduced in C99. It is
	249	provided as a GNU extension to C++98 in g++. This flag builds
	250	support for "long long" into the library (specialized
	251	templates and the like for iostreams). This option is on by default:
	252	if enabled, users will have to either use the new-style "C"
	253	headers by default (i.e., <cmath> not <math.h>)
	254	or add appropriate compile-time flags to all compile lines to
	255	allow "C" visibility of this feature (on GNU/Linux,
	256	the flag is -D_ISOC99_SOURCE, which is added automatically via
	257	CPLUSPLUS_CPP_SPEC's addition of _GNU_SOURCE).
	258	This option can change the library ABI.
5d5e5e4e	259	</p>
64a6f971	260	</dd>
572cd73a	261
1165dc50 PC	262	<dt><code>--enable-fully-dynamic-string </code></dt>
	263	<dd><p>This option enables a special version of basic_string avoiding
	264	the optimization that allocates empty objects in static memory.
	265	Mostly useful together with shared memory allocators, see PR
	266	libstdc++/16612 for details.
	267	</p>
	268	</dd>
	269
64a6f971	270	<dt><code>--enable-concept-checks </code></dt>
572cd73a PE	271	<dd><p>This turns on additional compile-time checks for instantiated
	272	library templates, in the form of specialized templates,
	273	<a href="19_diagnostics/howto.html#3">described here</a>. They
	274	can help users discover when they break the rules of the STL, before
	275	their programs run.
	276	</p>
64a6f971	277	</dd>
9aa43698	278
64a6f971	279	<dt><code>--enable-symvers[=style] </code></dt>
3cbc7af0	280
6aa43d99	281	<dd><p>In 3.1 and later, tries to turn on symbol versioning in the
3cbc7af0 BK	282	shared library (if a shared library has been
	283	requested). Values for 'style' that are currently supported
	284	are 'gnu', 'gnu-versioned-namespace', 'darwin', and
	285	'darwin-export'. Both gnu- options require that a recent
	286	version of the GNU linker be in use. Both darwin options are
	287	equivalent. With no style given, the configure script will try
	288	to guess if the 'gnu' style can be used, and if so, will turn
	289	it on.
9aa43698	290	</p>
3cbc7af0	291
64a6f971	292	</dd>
44f0760e	293
d8d81f62	294	<dt><code>--enable-libstdcxx-pch </code></dt>
44f0760e BK	295	<dd><p>In 3.4 and later, tries to turn on the generation of
	296	stdc++.h.gch, a pre-compiled file including all the standard
	297	C++ includes. If enabled (as by default), and the compiler
	298	seems capable of passing the simple sanity checks thrown at
	299	it, try to build stdc++.h.gch as part of the make process.
	300	In addition, this generated file is used later on (by appending <code>
	301	--include bits/stdc++.h </code> to CXXFLAGS) when running the
	302	testsuite.
	303	</p>
	304	</dd>
3660e02f PE	305
	306	<dt><code>--disable-hosted-libstdcxx </code></dt>
	307	<dd><p>By default, a complete <em>hosted</em> C++ library is built. The
	308	C++ Standard also describes a <em>freestanding</em> environment,
	309	in which only a minimal set of headers are provided. This option
	310	builds such an environment.
	311	</p>
	312	</dd>
5d5e5e4e	313	</dl>
5d5e5e4e	314	<p>Return <a href="#top">to the top of the page</a> or
0435269a	315	<a href="http://gcc.gnu.org/libstdc++/">to the libstdc++ homepage</a>.
5d5e5e4e	316	</p>
b2dad0e3 BK	317
	318
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	320
64a6f971	321	<hr />
0435269a	322	<p class="fineprint"><em>
c9fe10db	323	See <a href="17_intro/license.html">license.html</a> for copying conditions.
8ddad08b	324	Comments and suggestions are welcome, and may be sent to
0435269a	325	<a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>.
5d5e5e4e	326	</em></p>
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